Sodium-dependent multivitamin transporter deficiency (SMVTD) is an autosomal recessive multisystemic metabolic disorder with highly variable manifestations. Affected individuals usually present at birth or in infancy with severe feeding problems, gastrointestinal reflux, cyclic vomiting, and diarrhea associated with failure to thrive. Gastrointestinal hemorrhage may occur; tube-feeding is often required for a short time. The course and severity of the disease varies: some patients have episodes of acute metabolic decompensation during infection that respond well to treatment, whereas others show more permanent neurologic regression with loss of early motor and cognitive milestones in the first year or so of life. Less severely affected patients have normal development or mild growth and motor delays, whereas more severely affected individuals may have seizures, ataxia, spasticity, peripheral neuropathy, immune defects, and osteopenia. In severely affected patients, brain imaging shows cerebral, cerebellar, and brainstem atrophy and thin corpus callosum. Treatment with biotin, pantothenic acid, and alpha-lipoic acid has been shown to result in significant clinical improvement (Byrne et al., 2019; Hauth et al., 2022). [from OMIM]